Influence of Hydroxyls on Pd Atom Mobility and Clustering on Rutile TiO2(011)-2 x 1
Influence of Hydroxyls on Pd Atom Mobility and Clustering on Rutile TiO2(011)-2 x 1
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DOI：
10.1021/nn501817w
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发表时间：
2014-06-01
期刊：
影响因子：
17.1
通讯作者：
Batzill, Matthias
中科院分区：
文献类型：
--
作者：
Addou, Rafik;Senftle, Thomas P.;Batzill, Matthias
理解后过渡金属原子（例如Pd）在金属氧化物载体（例如TiO 2）上的附聚对于设计非均相催化剂以及通常控制金属/氧化物界面至关重要。减少颗粒烧结的一种方法是用降低吸附原子迁移率的羟基改性金属氧化物表面。我们通过扫描隧道显微镜实验、密度泛函理论（DFT）计算和蒙特卡罗（MC）计算机模拟研究了Pd在羟基改性的TiO 2（011）-2 x 1表面上烧结的原子过程。在羟基化表面上形成在室温下稳定的小的1-3原子簇，而在相同条件下在无羟基表面上形成大得多的簇。DFT表明，这是一个结果，更强的结合相邻的羟基和Pd原子的羟基化表面上的Pd原子的表面扩散势垒增加的Pd原子。DFT、动力学MC和基于ReaxFF的NVT-MC模拟表明，比单个Pd单体大的Pd团簇可以从氧化物表面吸附氢并形成Pd双金属。这耗尽了表面羟基覆盖，从而允许Pd在室温下更自由地扩散和团聚。实验上，这导致双峰簇尺寸分布，在低Pd覆盖率下普遍存在1-3个原子簇，而在较高Pd浓度下显著较大的簇成为主导。这项研究表明，羟基化的氧化物表面可以显着降低Pd簇的大小，从而使表面填充由单个到几个原子组成的金属簇的制备。
Understanding agglomeration of late transition metal atoms, such as Pd, on metal oxide supports, such as TiO2, is critical for designing heterogeneous catalysts as well as for controlling metal/oxide interfaces in general. One approach for reducing particle sintering is to modify the metal oxide surface with hydroxyls that decrease adatom mobility. We study by scanning tunneling microscopy experiments, density functional theory (DFT) calculations, and Monte Carlo (MC) computer simulations the atomistic processes of Pd sintering on a hydroxyl-modified TiO2(011)-2 x 1 surface. The formation of small 1-3 atom clusters that are stable at room temperature is achieved on the hydroxylated surface, while much larger clusters are formed under the same conditions on a hydroxyl-free surface. DFT shows that this is a consequence of stronger binding of Pd atoms adjacent to hydroxyls and increased surface diffusion barriers for Pd atoms on the hydroxylated surface. DFT, kinetic MC, and ReaxFF-based NVT-MC simulations show that Pd clusters larger than single Pd monomers can adsorb the hydrogen from the oxide surface and form Pd hydrides. This depletes the surface hydroxyl coverage, thus allowing Pd to more freely diffuse and agglomerate at room temperature. Experimentally, this causes a bimodal cluster size distribution with 1-3 atom clusters prevalent at low Pd coverage, while significantly larger clusters become dominant at higher Pd concentrations. This study demonstrates that hydroxylated oxide surfaces can significantly reduce Pd cluster sizes, thus enabling the preparation of surfaces populated with metal clusters composed of single to few atoms.